The present invention relates to electrical switches and, more particularly, to an electromagnetic bi-stable switch using fault current induced electromagnetic force to maintain switch closure.
In electrical control systems for electric motor powered vehicles such as locomotives, it is common to utilize electric power isolation switches to carry very large fault currents, e.g., currents in the range of 100,000 amperes. In stationary applications, large mechanical disconnect switches (i.e., knife switches) can be utilized for this purpose. However, in transportation applications, such as locomotives, transit cars or off-highway vehicles, such isolation or disconnect switches are required to be small in size and lightweight. Furthermore, the breaker must have a relatively long life cycle, e.g., 20,000 cycles without replacement. These switches are distinct from circuit breakers in that they are designed to maintain contact closure for very large currents whereas circuit breakers are generally designed to open under high current conditions.
One problem with such high-current switches is that current constriction at a contact can generate very high separation forces on a closed contact. For example, 100,000 amperes can generate about 2244 pounds of force on a single butt contact. Accordingly, it is desirable to provide a relatively small isolation switch that can withstand very large currents and can be cycled repetitively.